1. Field of the Invention
The present invention relates to a transmission for a vehicle, more particularly, to a constant-mesh type transmission for a vehicle in which plural transmission shafts each of which supports plural transmission gears in a row are arranged in parallel so that mutually corresponding transmission gears are engaged.
2. Description of Background Art
For a conventional type transmission for a bicycle, as disclosed in Japanese published unexamined patent application No. Hei9-249183, a planetary gear type transmission is provided with a hub spindle (a sun gear) fastened to a bicycle frame so that the hub spindle is not turned. A hub flange is attached to the periphery of the hub spindle so that the hub flange can be rotated. Plural gears (planetary gears) are provided between the hub spindle and the hub flange wherein pedal effort transmitted to a chain sprocket is varied at multiple stages by the plural planetary gears and each clutch mechanism and is transmitted to the hub flange is known. An actuator for fitting a ratchet one-way mechanism of the clutch mechanism or releasing the fitting is inserted into the hub spindle, and the fitting of the ratchet one-way mechanism and the release of the fitting are executed by revolving the actuator around the hub spindle by a predetermined angle.
The planetary gear type transmission is composed of multiple parts. Thus, the transmission efficiency is low and axial downsizing is particularly difficult because the multiple parts are axially arranged. Therefore, for a transmission for a bicycle the limit of the width is severe. Thus, the conventional type of transmission is not desirable.
In the prior art described above, as the actuator for fitting the ratchet one-way mechanism of the clutch mechanism or releasing the fitting is cylindrical and is required to be turned by a predetermined angle on the periphery of the spindle, it is difficult to apply the prior art to a transmission in which a spindle itself is rotated. Further, in the prior art, the actuator cannot be turned in a state in which torque is applied and the shift is disabled.